1. Field of the Invention
The present invention relates to a photographic lens system mainly for use in an electronic still camera having a charge-coupled device (CCD).
2. Description of the Related Art
In a miniature CCD camera such as an electronic still camera, due to advancements in CCD production technologies, a size of pixel has been reduced, so that a CCD with great high-density to the point of approximately one million pixels has been utilized. Accordingly, in order to correspond to such a high-density CCD, the CCD camera requires a photographic lens system having very high resolution and high optical performance. Furthermore, along with the pursuit of improved optical performance, there is a strong demand for further miniaturization and cost reduction. Also, in a CCD camera for color photography, in order to prevent irregular color distribution, the so-called telecentricity of incident light rays is required, i.e., the light rays emitted through the photographic lens system are made incident on the CCD as perpendicular as possible. In addition, in a CCD camera, since optical elements such as a low-pass filter and an infrared-cut filter have to be installed in a space provided between the photographic lens system and the CCD, a sufficiently long back focal distance is required.
In photographic lens systems of the prior art utilized in CCD cameras, the above-mentioned requirements are not simultaneously and sufficiently met, which has left room for improvement.